The present disclosure relates generally to the field of display optics. More specifically, the disclosure relates to substrate guided optics.
Conventional solutions for wide field of view Head Mounted Displays (HMDs) (e.g., a helmet mounted display) and Head Up Displays (HUDs) generally include off-axis visors, combiners, and multiple complex tilted and decentered lenses. The field of view that can be achieved with conventional fixed diffractive components may be limited to less than about 30 degrees external angle. This limited field of view may not meet requirements for digital night vision systems and wide field of view HUDs or HMDs.
Conventional HMD optical designs, such as those for the Joint Helmet Mounted Cueing System (JHMCS), the Joint Strike Fighter (JSF), and the Eurofighter Typhoon, use complex tilted and decentered, aspheric plastic lenses. For example, the JSF HMD incorporates seven lenses in order to correct the off-axis aberrations induced by the visor. These lens elements are expensive, tolerance limited, and require precision tooling to assemble.
The optical performance of conventional visor-projected designs, typically fall off with exit pupil and field of view and barely meet the Modulation Transfer Function (MTF) performance required for night vision sensors.
A reduction in mass at the HMD system level is desirable for a number of reasons. To establish the effects of head supported mass during flight, the mass is multiplied by the aircraft acceleration. For high performance fighter aircraft pulling a 10 G turn, the mass of the HMD is multiplied by 10. Head supported mass also affects the induced neck loads during parachute deployment, HMD components, especially the optics, tend to be oriented forward and upward in the helmet. Neck strain during normal flight can be exacerbated by this forward center of mass, for example, induced neck forces during ejection and parachute deployment may be worsened by an upward and forward center of mass.
What is needed is an optical system having a lower mass. What is also needed is an optical system that does not need an IPD adjustment mechanism. What is also needed is an optical system having a smaller volume lens system. What is further needed is an optical system having a smaller volume display module. What is further still needed is an optical system having a lower cost. What is further still needed is an optical system without the need for a custom fit system.